Sub-miniature snap-acting switch



Feb. 8, 1966 F. G. MCCLOSKEY 3,2343% SUB-MINIATURE SNAP-ACTING swmca Filed April 10, 1962 PRIOR ART INVENTOR 66 PEN/MORE 6. Mc CLOSKE) /J7///////// J FIG'aA /W, M96926? ATTORNEYS United States Patent 3,234,343 SUB-MINIATURE SNAPACTING SWITCH Fenirnore G. Mcfiioslrey, Coiurnhus, Ohio, assignor to Columbus Electric Manufacturing Co., Columbus, Ohio, a corporation of Ohio Filed Apr. 10, 1962, Ser. No. 186,453 Claims. (Cl. 200-67) This invention relates to switches and, more specifically, to improved miniature snap-acting switches.

There has heretofore been a long and continuous need for the smallest possible components to perform various electrical functions. Moreover, in the case of electric switches actuated by mechanical movement as by displacement of an actuator member, many severe conditions are imposed upon selection of a suitable switch mechanism and over-all switch design such as long switch life and low operating forces, for example.

Prior art switches that have been characterized as subminiature have had relatively high operating forces in the 410 ounce range and small travel of the actuator member. A typical total excursion of this member in the prior art switches has been only 0.050 to 0.075 inch, and overtravel has been limited to 0.006 to 0.008 inch. Also, the particular switch mechanisms employed have useful lives far less than the larger sized snap-acting switch mechanisms, and the use of the prior art sub-miniature switches has therefore been unacceptable for applications requiring long switch life.

In accordance with the present invention, it has been found that a particular type of prior art snap-acting switch, previously commercially available in larger than sub-miniature size, can be shrunk to a size equal to, and/ or even smaller in certain dimensions, than the prior art sub-miniature switches without significant sacrifice in operating characteristics. The new miniaturized snapacting switch of the present invention has a mechanical life that is nearly twice the mechanical life of the prior art sub-miniature switches; it may have an operating force of as little as one ounce; it may accommodate total actuator member excursions of from 0.100 to 0.150 inch with overtravels of 0.010 to 0.015 inch, and it may be made about one-third thinner than the prior sub-miniature switches.

Accordingly, it is the object of this invention to provide an improved sub-miniature switch having the foregoing operating and size characteristics.

Another object is to provide a novel miniaturized Version of a known type of snap-acting switch that can be used successfully as a sub-miniature switch.

A further object is to provide a novel sub-miniature switch that has a U-shaped actuator member and a push button contacting said member at an impact point with the actuating member having a novel reinforcing cross section to avoid coincidence of the zone of maximum stress and the impact point.

Other objects and novel features of the present invention will become fully apparent from the appended claims and from the ensuing detailed description and discussion as it proceeds in conjunction with the accompanying drawings in which:

FIGURE 1 is a front elevation of a prior art standard size snap-acting switch with a housing side cover removed to illustrate the configuration and arrangement of the operating switch components;

FIGURE 2 is an end elevation of the switch of FIG- URE 1;

FIGURE 3 is a front elevation of the novel sub-miniature snap-acting switch of the present invention with a housing side cover removed to illustrate its internal components;

FIGURE 3A is a view in section of the switch actuating member of FIGURE 3 taken along line 3A3A of FIG- URE 3;

FIGURE 4 is an end elevation of the switch of FIGURE FIGURE 5 is a front elevation, with a housing side cover removed, of another embodiment of a sub-miniature snap-acting switch constructed in accordance with the principles of the present invention;

FIGURE 6 is a front elevation with a housing side cover removed, of yet another embodiment of a sub-miniature snap-acting switch constructed in accordance with the present invention;

FIGURE 7 is a front elevation of still a further embodiment of a sub-miniature snap-acting switch which may be constructed in accordance with the present invention; and

FIGURE 8 is an end elevation of the switch housing shown in FIGURES 6 and7.

Referring now to the drawings, the novel sub-rniniature snap-acting switches of the present invention, illustrated in FIGURES 38, may have substantially the same construction as larger prior art, snap-acting switches. The switch embodiments. shown in FIGURES 3-5 are similar to the prior art snap-acting switch 10 illustrated in FIG- URES l and 2 which is disclosed and claimed in copending United Statesapplication No. 35,389, filed. June 7, 1960.

Switch 16, which is representative of the general type that, ithas been found, can be shrunk to sub-miniature size in accordance with this invention, consists generally of a substantially rectangular housing or base 12 provided with through apertures 14 at each of its corners for receiving suitable fasteners formounting the switch and for securing a side cover (not illustrated) in place. Switch housing 12 has a length of. approximately 1.19 inches, a width of approximately 0.81 inch, and a thickness of approximately 0.28 inch (see FIGURE 2). Other prior art switches having snap-acting mechanisms like those illustrated in FIGURES 6 and 7 are commercially available in housings that have dimensions almost identical to those shown in FIGURES l and 2.

Housing 12 includes an upper contact support portion 16 and a lower contact support portion 18. A central projecting nose com-prising bosses or backing portions 20 and 22 is disposed between upper and lower contact support portions 16 and-18 to define upper and lower channels which receive upper and lower fixed contact arms 24 and 26. A similar channel is provided between bosses 20 and 22 to receive a central, movable contact arm assembly 28.

Inside of the housing cavity, further upper and lower channels 30 and 32, which are symmetrical about the horizontal center line of the switch housing andwhich have channel extensions 34 and 35 directed toward the respective fixed contact arms, are provided for receiving the ends of the switch actuating member 38. A vertical through bore is provided in the upper housing wall 42 to receive a slidably mounted, actuating push button 44.

Upper fixed contact arm 24 is made of a suitable metal and of a sufficient size to be rigid. The usual contact 46 is provided at its inner end and a suitable terminal aperture 48 is provided at its outer end. Lower contact arm 26 is formed in the same manner as upper contact arm 24- and has a contact 50 and a terminal aperture 52.

Movable contact arm assembly 28 includes a terminal aperture 53 and a flexible contact arm 54- which is formed from a suitable resilient metal such as beryllium copper and which has contacts 56 and 58 secured on its opposite sides facing contacts 46 and 50.

At the right side of contacts 56 and 58 an abrupt deformation or bend 60 is formed in contact arm 54 to.

provide an arched or arcuate portion 62. Since arcuate portion 62 is made of a resilient material, the force at bend 60 always urges one of the contacts 56 or 68 into engagement with the associated fixed contact. Which contact is engaged by the associated movable contact depends upon whether the free end 64 of arcuate contact arm portion 62 is below or above the horizontal center line of the switch between fixed contacts 46 and 50.

Actuating member 38, which is substantially U-shaped, has an upper leg 66 and a lower leg 68. The free ends of these legs are bent at right angles to secure actuating member 38 in channel extensions 34 and 36. Suflicient clearance is provided so that the only contact which actuating member 38 has with housing 12 is in the channels 30 and 32.

End section 70 of actuating member 38 is provided with a stiffening rib or r-idge 72. The pointed free end 64 of arcuate contact arm portion 62 is positioned at the bottom 74 of the depression forming the stiffening ridge 72. A simple frictional connection is thus provided which retains the contact arm section 62 in the desired arched form and which causes its free end 64 to move up and down with the central section 70 of switch actuating member 38. Other types of connections, such as a tongue and groove connection, may be used instead of the friction connection described above, if desired.

In operation, when actuating push button 44 is pressed downwardly, legs 66 and 68 of main actuating member 38 are flexed with bending occurring in the upper and lower legs near the fixed points in channel extensions 34 and 36 and flexing occurring in its curved sections 76 and 78. Since upper leg 66 and lower leg 68 are, in effect, rigid links of constant length, the upper end of curved section 78 moves in an arcuate path about a fixed point near channel extension 34. Since the bend of leg 66 is substantially a right angle in channel extension 34, curved section 76 has a slight component of movement inwardly toward the switch contacts.

Lower leg 68 of main actuator member 38 is disposed at an angle of slightly less than 90 to the direction of movement of actuator leg 66 about its pivot point in channel extension 36. Consequently, curved section 78 has a slight component of movement away from th switch contacts in an arcuate path about a fixed point in channel extension 36. End section 70 of theactuator member 38 is in effect a rigid link. Thus, although there is a slight component of movement toward the switch components at the upward end of section 70 and a slight component of movement away from the switch contacts at its lower end,,the plotted path of end 64 of arcuate contact arm portion 62 is a substantially straight line.

The curved portion 78 of the actuator member is spaced a distance from surface 79 of the switch housing such that a large total excursion of push button 44, including a substantial overtravel, can be accommodated without damage to the switch mechanism. Additional details of the abovedescribed switch assembly are discussed in the copending application referred to above to which reference may be had if deemed necessary.

FIGURES 3 and 4 illustrate a miniaturized version of the snap-acting switch described above in connection with FIGURES 1 and 2 which has been reduced to a size comparable to or less than that of the prior art subminiature switches. As shown in FIGURE 4, the thickness of this switch is 0.17 inch as compared with the thickness of the prior art sub-miniature switches of about 0.25 inch and with the thickness of the prior conventional size snap-acting switches of about 0.28 inch. The length of the sub-miniature switch of FIGURE 3 is about 0.56 inch as compared with the length of the conventional snap-acting switch of FIGURE 1 of 1.19 inches, and the width of the switch of FIGURE 3 is 0.50 inch as compared with the width of the switch of FIGURE 1 of 0.81 inch.

The materials used in the sub-miniature switch of FIG- URES 3 and 4 are the same as the materials used in the full-sized snap-acting switch of FIGURES 1 and 2. However, the thicknesses of the switch mechanism components, particularly beryllium copper actuator members, have been significantly reduced because of the smaller dimensions involved. The center contact arm 54 and actuate portion 62 are integral as described in the embodiment of FIGURE 1 and the actuating member 38 has a U-shaped configuration with a rigid upper leg 66 corresponding to upper leg 66 in the embodiment of FIG- URE 1.

The only significant change in structural configuration of any of the parts is that the cross-sectional configuration of upper leg 66 of actuating member 38 is formed without the central rib 82 shown in the embodiment of FIG- URE 1. The end of the rib is the weakest point of leg 66 since the material is stressed the most at this point. This construction is poorly suited for a sub-miniature switch because push button 44 contacts leg 66 at a point substantially coincidental with the end of the stiffening rib and this becomes the first part in the sub-miniature switch to fail. Because actuator member leg '66 is desir-ably made as thin and narrow as possible to provide maximum size reduction of the switch, upper actuator leg 66 is formed with a channel-like cross-sectional configuration (see also FIGURE 3A) which imparts the requisite stiflness to the leg and eliminates the weak point resulting from the stamping of a rib into the mern The embodiment shown in FIGURE 5 dififers from the embodiment shown in FIGURE 3 primarily by the configuration and shape of the contact support portions 16 and 18.

In both embodiments the housing is provided with a sloping surface 79 beneath the portion of the actuating member below arcuate section 62 of the flexible contact arm 54 which permits displacement of push button 44 downwardly to a position flush with the upper outer surface of housing 10, providing an increased total actuator member excursion. The spacing between fixed contacts 46 and 50 determines the operating differential between total push button excursion and push button overtraveii which is normally adjusted so that there is an overtravel of push button 44 beyond the position where the movable" contacts on arm 54 transfer from one fixed contact to the other that is at least 10% of the total excursion.

In contrast with the prior art sub-miniature switches, which require operating forces of about 4 to 10 ounces, the novel sub-miniature snap-acting switch 80 of the present invention thus constructed may be operated with actuating forces of as little as one ounce. And, by em loymg the type of snap-acting switch mechanisms shown herein, the total excursion of the actuator member may be increased to a range of 0.10 to 0.15 inch which compares favorably with the prior art conventional sized snapacting switches and which is nearly double the total excursion of the prior art sub-miniature switches. Additionally, an overtravel on the order of 10% of the total excursion can be accommodated by the sub-miniature switch housing of the present invention. This overtravel amounts to roughly 0.010 to 0.015 inch and is about twice the overtravel that can be accommodated by prior art sub-miniature switch housings. Further, the mechanicah life of the sub-miniature switch of the present invention; is substantially double that of the prior art sub-miniature; switches and compares favorably with the mechanical life: of the conventional size snap-acting switches using a simi.* lar switch actuating mechanism.

Another important feature of the sub-miniature switch: provided by the present invention is that the location: of the push button may be varied relative to the main actuator member to change the fulcrum and thereby" make available various combinations of actuating forces: and actuator excursions. This provides versatility whichv is unique in sub-miniature switches. In the embodiment of FIGURE 5, for example, push button 44 may be positioned at any point along the upper leg of actuator 38 between the locations shown in sol-id and in dotted lines. The position of the push buttons of FIGURES 3, 6, and 7 may be similarly varied as desired. Because of the novel sub-miniature switch construction provided, variations in push button position do not adversely affect the increased overtravel or other advantages of the sub-miniature switch of the present invention.

Other types of snap-acting switch mechanisms may also be shrunk to provide miniaturized versions of the size of the conventional sub-miniature switch. FIG- URE 6 illustrates a miniaturized version of one commerically available standard size snap-acting switch of this type. The contact carrying arm 88 which is centrally disposed between two fixed contact arms 90 and 92 is actuated by a Z-shaped member 94 that is connected at opposite ends by a tongue and slot arrangement to arm 88 and to the free end 95 of actuator member 98. Actuator member 98 has an L-shape and is anchored .at one end to the switch housing 100. The actuator member is provided with a suitable stilfening means such as sleeves 102 so that free end 96 is movable in a substantially vertical direction by depression of button 104 to cause transfer of the switch contacts. The switch actuating mechanism shown in FIGURE 6 contains the features which make it adaptable for reduction to subminiature size with the advantages also present in the switch embodiments shown in FIGURES 3-5.

FIGURE 7 illustrates a further form of snap-acting switch which is available commercially in the standard size (i.e. with the dimensions shown in FIGURES 1 and 2) and the snap-acting mechanism of which is disclosed in United States Patent No. 2,553,219. This switch may also be shrunk to a sub-miniature size in accordance with the principles of the present invention. In this switch embodiment, an arcuate or rolling spring member 198 is slotted at opposite ends to receive tongues 110 and 112 on the free ends of resilient arm 114 and actuating member 116, respectively. Actuating member 116 has an L-shape and is anchored at one end to the switch housing. A push button 120 is provided for causing-downward movement of actuator member 16 to transfer the switch contacts. In this embodiment, as well as in other embodiments shown herein, a substantial total excursion of actuating arm 116 and button 120 is provided together with the space necessary to accommodate the desirable degree of overtravel as discussed in connection with the switches shown in FIGURES 3-5. The advantages of light operating force and long life are also provided by this switch embodiment,

FIGURE 8 is an end elevation of either (or both) of the switches of FIGURE 6 and FIGURE 7. The thickness of these switches may be on the order of 0.20 inch. The length of these switch embodiments may be reduced to no greater than 0.75 inch and the width to no greater than about 0.50 inch.

The present invention is not based solely on mere reduction in size of a prior art switch, but upon the discovery that a particular type of snap-acting switch, out of literally scores of switch constructions that have been and are now presently on the market, can be successfully shrunk to a sub-miniature size, The volume of the new sub-miniature switch housing (about 006 cubic inch) is less than oneefourth the volume of the housing (about 0.25 cubic inch) of the same standard size snap-acting switch mechanism, a reduction of over 75%. The sub-miniature snap-acting switch of this invention provides greatly improved results compared to the prior art sub-miniature switch constructions because (in large part) of the unique actuating member construction which permits lower operating forces and 6 larger total actuator member excursions, and because of the disposition of the snap-acting switch mechanism between the actuating member and the contacts on the central resilient arm. The mechanical life of the switch of the present invention is approximately double the mechanical life of the prior art sub-miniature switches.

What is claimed is:

1. A snap-acting switch of sub-miniature size, com

prising:

(a) a miniaturized housing having parallel side walls spaced by top, bottom, and end walls, said housing having an exterior length no greater than about 0.75 inch, an exterior width no greater than about 0.50 inch, and an exterior thickness no greater than about 0.20 inch;

(b) a pair of elongated, spaced, substantially rigid, cantilevered contact arms secured to one of said end Walls and extending toward the other end wall;

(c) fixed contacts on the facing surfaces of said rigid contact arms at the free ends thereof;

(d) a resilient, elongated contact arm extending between said rigid arms and secured to said one end wall;

(e) movable contacts mounted on the opposite surfaces of said resilient contact arm and positioned to alternatively engage one or the other of said fixed contacts;

(f) means including an actuator member mounted for movement in a direction perpendicular to the centerline of said resilient arm for controlling movemeut thereof, said actuator member having an upper leg of downwardly facing channel-like cross-sectional configuration;

(g) means coupling the resilient contact arm to the actuator member at a position between the actuator member and the movable contacts for efiecting a snap movement of the resilient arm to move the disengaged movable contact into engagement with the associated fixed con-tact;

(l1) integral backing portions extending from said one end wall between said resilient contact arm and each of the rigid contact arms toward the other end wall; and

(i) integral contact support portions extending from said one end wall along the opposed surfaces of said rigid contact arms towards said other end wall.

2. A snap-acting switch of sub-miniature size, comprising:

(a) a miniaturized housing of lightweight rigid plastic having parallel side walls spaced by top, bottom, and end walls, said housing having an exterior length and with 'no greater than about 0.75 and 0.50 inch, respectively, and a thickness less than said width;

(b) a pair of elongated, spaced, substantially rigid, cantilevered contact arms secured to One of said end walls and extending towards the other end wall;

(0) fixed contacts, on the facing surfaces of said rigid contact arms at the free ends thereof;

(d) a resilient, elongated contact arm extending be tween said rigid arms and secured to, Said one and W l (e) movable contacts mounted on the opposite surfaces of said resilient contact arm and positioned to altere y g ge on or the o er of said fixed contaets;

( me ns in g an a t a or mem er mounted for movement in the plane d fined by the longitudinal centerlines of said rigid and resilient contact arms and in a direction perpendicular to the centerlines of said resilient arm for controlling movement thereof, said actuator member having a leg substantially parallel to said housing top and bottom walls with one end anchored to said housing and the other end free to move in said plane, said actuator member also having a total excursion of about 0.10 to 0.15

inch with an overtravel of one-tenth of the excursion, being permissible;

(g) means coupling the resilient contact arm to the actuator member at a position between the actuator member and the movable contacts for effecting a snap movement of the resilient arm to move the disengaged movable contact intoengagement with the associated fixed contact;

(h) means for limiting to no greater than about one ounce the required external force applied to said actuator leg adjacent said movable end for effecting said snap movement;

(i) integral backing portions extending from said one end wall between said resilient contact arm and each of the rigid contact arms toward the other end wall; and

(j) integral contact support portions extending from said one end wall along the opposed surfaces of said rigid contact arms toward said other end wall.

'3. The switch as defined in claim 2, wherein the actuator member is U-shaped with free ends anchored to said housing and opposite legs on the sides of the fixed contact arms away from the sides thereof adjacent the resilient arm together with means extending through a housing wall and in abutting relation to one leg of said actuator member for imparting switching motion to said actuator member.

4. A snap-acting switch of sub-miniature size, comprising:

(a) a miniaturized housing having parallel side walls spaced by top, bottom, and end walls, said housing having an exterior length of no greater than about 0.75 inch, an exterior width no greater than about 0.50 inch, and an exterior thickness no greater than 0.20 inch;

(b) a pair of elongated, spaced, substantially rigid, cantilevered contact arms secured to one of said end walls and extending towards the other end wall;

(0) fixed contacts on the facing surfaces of said rigid contact arms at the free ends thereof;

(d) a resilient, elongated contact arm extending between said rigid arms and secured to said one end wall;

(e) movable contacts mounted on the opposite surfaces of said resilient contact arm and positioned to alternatively engage one or the other of said fixed contacts;

(f) means including an actuator member mounted for movement in the plane defined by the longitudinal centerlines of said rigid and resilient contact arms and in a direction perpendicular to the centerline of said resilient arm for controlling movement thereof, one end of said actuator member being fixed to said one end wall;

(g) means coupling the resilient contact arm to the actuator member at a position between the actuator member and the movable contacts for effecting a snap movement of the resilient arm to move the disengaged movable contact into engagement with the associated fixed contact;

(h) means extending through said top wall adjacent said other end wall for activating said actuator member to effect said resilient arm snap movement;

(i) means for limiting the resistance to the eifecting of said snap movement to a force no greater than about one ounce applied to the free end of said actuator through said activating means;

(j) integral backing portions extending from said one end wall between said resilient contact arm and each of the rigid contact arms toward said other end wall;

(k) integral contact support portions extending from said one end wall along the opposed surfaces of said rigid contact arms toward said other end wall; and

(1) means providing a first switch mounting aperture extending between and opening onto the exterior surfaces of said parallel side walls adjacent the intersection of said bottom wall and said other end wall;

(in) means providing a second mounting aperture extending between and opening onto the exterior surfaces of said parallel side walls adjacent the intersection of said one end wall and said top wall, said first and second mounting apertures being the only mounting apertures provided in said housing;

(11) first integral backing portions extending from said One end wall between said resilient contact arm and each of the rigid contact arms toward the other end wall; and

(0) second integral backing portions extending from said one end wall along the opposed surfaces of said rigid contact arms toward said other end wall.

5. A snap-acting switch of sub-miniature size, as defined in claim 4, said actuator member has a total excursion of about 0.10 inch.

References Cited by the Examiner UNITED STATES PATENTS 2,728,826 12/1955 Lauder 20067 2,839,629 6/1958 Korsgren 20067 2,993,101 7/1961 B-al l, et al. 200-67 2,993,102 7/1961 Anderson et a1 20067 FOREIGN PATENTS 1,238,609 7/1960 France.

850,104 9/ 1960 Great Britain.

BERNARD A. GILHEANY, Primary Examiner. ROBERT K. SCHAEFER, Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,234,343 February 8, 1966 Penimore G. McCloskey ertified that error appears in the above numbered pat- It is hereby c ection and that the said Letters Patent should read as ent requiring corr corrected below.

Column 4, line 7, for "actuate" read arcuate colum 6, line 52, for "with" read width Signed and sealed this 7th, day of February 1967.

(SEAL) Attest:

ERNEST W. SWIDER Attesting Officer EIWWARD L BRENPHH Commissioner of Patents 

1. A SNAP-ACTING SWITCH OF SUB-MINIATURE SIZE, COMPRISING: (A) A MINIATURIZED HOUSING HAVING PARALLEL SIDE WALLS SPACED BY TOP, BOTTOM, AND END WALLS, SAID HOUSING HAVING AN EXTERIOR LENGTH NO GREATER THAN ABOUT 0.75 INCH, AN EXTERIOR WIDTH NO GREATER THAN ABOUT 0.50 INCH, AN EXTERIOR THICKNESS NO GREATER THAN ABOUT 0.20 INCH; (B) A PAIR OF ELONGATED, SPACED, SUBSTANTIALLY RIGID, CANTILEVERED CONTACT ARMS SECURED TO ONE OF SAID END WALLS AND EXTENDING TOWARD THE OTHER END WALL;: (C) FIXED CONTACTS ON THE FACING SURFACES OF SAID RIGID CONTACT ARMS AT THE FREE ENDS THEREOF; (D) A RESILIENT, ELONGATED CONTACT ARM EXTENDING BETWEEN SAID RIGID ARMS AND SECURED TO SAID ONE END WALL; (E) MOVABLE CONTACTS MOUNTED ON THE OPPOSITE SURFACES OF SAID RESILIENT CONTACT ARM AND POSITIONED TO ALTERNATIVELY ENGAGE ONE OR THE OTHER OF SAID FIXED CONTACTS; (F) MEANS INCLUDING AN ACTUATOR MEMBER MOUNTED FOR MOVEMENT IN A DIRECTION PERPENDICULAR TO THE CENTERLINE OF SAID RESILIENT ARM FOR CONTROLLING MOVEMENT THEREOF, SAID ACTUATOR MEMBER HAVING AN UPPER LEG OF DOWNWARDLY FACING CHANNEL-LIKE CROSS-SECTIONAL CONFIGURATION; (G) MEANS COUPLING THE RESILIENT CONTACT ARM TO THE ACTUATOR MEMBER AT A POSITION BETWEEN THE ACTUATOR MEMBER AND THE MOVABLE CONTACTS FOR EFFECTING A SNAP MOVEMENT OF THE RESILIENT ARM TO MOVE THE DISENGAGED MOVABLE CONTACT INTO ENGAGEMENT WITH THE ASSOCIATED FIXED CONTACT; (H) INTEGRAL BACKING PORTIONS EXTENDING FROM SAID ONE END WALL BETWEEN SAID RESILIENT CONTACT ARM AND EACH OF THE RIGID CONTACT ARMS TOWARD THE OTHER END WALL; AND (I) INTEGRAL CONTACT SUPPORT PORTIONS EXTENDING FROM SAID ONE END WALL ALONG THE OPPOSITE SURFACES OF SAID RIGID CONTACT ARMS TOWARDS SAID OTHER END WALL. 